Mercurial > dropbear
annotate src/pk/dsa/dsa_verify_key.c @ 222:36160290a1b2 libtomcrypt LTC_DB_0.46
* change include path of options.h
* don't use the constant ROL/ROR operations, since compilers
seem to have problems
author | Matt Johnston <matt@ucc.asn.au> |
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date | Fri, 08 Jul 2005 19:13:24 +0000 |
parents | 39d5d58461d6 |
children |
rev | line source |
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
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2 * |
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3 * LibTomCrypt is a library that provides various cryptographic |
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4 * algorithms in a highly modular and flexible manner. |
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5 * |
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6 * The library is free for all purposes without any express |
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7 * guarantee it works. |
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8 * |
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9 * Tom St Denis, [email protected], http://libtomcrypt.org |
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10 */ |
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11 #include "tomcrypt.h" |
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12 |
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13 /** |
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14 @file dsa_verify_key.c |
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15 DSA implementation, verify a key, Tom St Denis |
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16 */ |
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17 |
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18 #ifdef MDSA |
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19 |
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20 /** |
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21 Verify a DSA key for validity |
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22 @param key The key to verify |
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23 @param stat [out] Result of test, 1==valid, 0==invalid |
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24 @return CRYPT_OK if successful |
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25 */ |
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26 int dsa_verify_key(dsa_key *key, int *stat) |
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27 { |
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28 mp_int tmp, tmp2; |
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29 int res, err; |
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30 |
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31 LTC_ARGCHK(key != NULL); |
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32 LTC_ARGCHK(stat != NULL); |
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33 |
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34 /* default to an invalid key */ |
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35 *stat = 0; |
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36 |
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37 /* first make sure key->q and key->p are prime */ |
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38 if ((err = is_prime(&key->q, &res)) != CRYPT_OK) { |
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39 return err; |
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40 } |
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41 if (res == 0) { |
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42 return CRYPT_OK; |
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43 } |
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44 |
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45 |
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46 if ((err = is_prime(&key->p, &res)) != CRYPT_OK) { |
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47 return err; |
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48 } |
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49 if (res == 0) { |
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50 return CRYPT_OK; |
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51 } |
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52 |
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53 /* now make sure that g is not -1, 0 or 1 and <p */ |
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54 if (mp_cmp_d(&key->g, 0) == MP_EQ || mp_cmp_d(&key->g, 1) == MP_EQ) { |
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55 return CRYPT_OK; |
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56 } |
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57 if ((err = mp_init_multi(&tmp, &tmp2, NULL)) != MP_OKAY) { goto error; } |
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58 if ((err = mp_sub_d(&key->p, 1, &tmp)) != MP_OKAY) { goto error; } |
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59 if (mp_cmp(&tmp, &key->g) == MP_EQ || mp_cmp(&key->g, &key->p) != MP_LT) { |
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60 err = CRYPT_OK; |
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61 goto done; |
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62 } |
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63 |
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64 /* 1 < y < p-1 */ |
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65 if (!(mp_cmp_d(&key->y, 1) == MP_GT && mp_cmp(&key->y, &tmp) == MP_LT)) { |
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66 err = CRYPT_OK; |
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67 goto done; |
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68 } |
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69 |
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70 /* now we have to make sure that g^q = 1, and that p-1/q gives 0 remainder */ |
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71 if ((err = mp_div(&tmp, &key->q, &tmp, &tmp2)) != MP_OKAY) { goto error; } |
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72 if (mp_iszero(&tmp2) != MP_YES) { |
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73 err = CRYPT_OK; |
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74 goto done; |
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75 } |
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76 |
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77 if ((err = mp_exptmod(&key->g, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; } |
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78 if (mp_cmp_d(&tmp, 1) != MP_EQ) { |
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79 err = CRYPT_OK; |
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80 goto done; |
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81 } |
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82 |
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83 /* now we have to make sure that y^q = 1, this makes sure y \in g^x mod p */ |
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84 if ((err = mp_exptmod(&key->y, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; } |
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85 if (mp_cmp_d(&tmp, 1) != MP_EQ) { |
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86 err = CRYPT_OK; |
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87 goto done; |
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88 } |
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89 |
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90 /* at this point we are out of tests ;-( */ |
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91 err = CRYPT_OK; |
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92 *stat = 1; |
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93 goto done; |
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94 error: err = mpi_to_ltc_error(err); |
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95 done : mp_clear_multi(&tmp, &tmp2, NULL); |
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96 return err; |
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97 } |
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98 #endif |
209 | 99 |
100 /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_verify_key.c,v $ */ | |
101 /* $Revision: 1.3 $ */ | |
102 /* $Date: 2005/05/05 14:35:59 $ */ |